The present invention relates to a lens and an optical composite structure, in particular, to a lens capable of being integrated with an additional optical device such as optical filter, and to an optical composite structure fabricated by integrating such a lens with an additional optical device.
In optical filter modules such as optical synthesizers, splitters and equalizers and other optical modules such as optical isolators and circulators that are used in optical communication technology, used is an optical composite structure in which a convex microlens for light collimation, convergence or expansion is optically connected with an additional optical device, for example, with an optical filter.
For optically connecting the convex lens with the other optical device in such optical modules, generally employed is a technique of accurately controlling the relative position of the convex lens and the other optical device for reducing the light loss through them, and fixing them in the respective holders such as cases. However, the process requires accurate position control, which causes low productivity and high production costs.
To solve the problem, used is a refractive index-distributed lens for optical collimation, and this is integrated with an additional optical device. Since such a refractive index-distributed lens exhibits its lens function on the basis of the refractive index profile thereof, its face through which it receives and emits light can be planarized. Accordingly, when an additional optical device is airtightly bonded to the planarized face of the lens of the type and when the outer periphery of the bonded area of the two is coated with an adhesive and the adhesive is cured, then the relative position of the lens and the optical device to be bonded thereto can be accurately controlled and the two can be well bonded and fixed.
Naturally, however, refractive index-distributed lenses are not easy to produce just as it is designed. Therefore, for refractive index-distributed lenses of an ordinary type which do not have a convex face and which exhibit their lens function only on the basis of their refractive index profile, it is difficult to have the intended optical characteristics including the optical path, and so on. Another problem with the lenses of the type is that they are unfavorable for small-sized appliances since they require a predetermined or more length for exhibiting their lens function.
Still another problem is that the uncured adhesive applied to such a refractive index-distributed lens and an optical device to be bonded thereto with it will often penetrate into the interface of the two bonded with it, owing to its capillary action. Still another problem is that the additional optical device may often meet a refractive index-distributed lens at some angles at their interface at which they are bonded, thereby forming a gap between the lens and the additional optical device. If so, an uncured adhesive for bonding them will penetrate into the gap. When the adhesive reaches the center part of the bonded area of the two, including the optical path of the lens, it will block the optical path and thereby enlarges the optical loss in the bonded structure. Depending on the temperature change in service condition, the adhesive having penetrated into the interface of the bonded structure will expand or shrink, therefore often causing misregistration of the optical device relative to the lens, or as the case may be, the constitutive components of the structure will be brought into contact with each other to generate stress that further enlarges the optical loss through the structure.
To solve the problems, an adhesive of high viscosity may be used for preventing it from penetrating into the bonded area. However, even when the adhesive of the type is used, it is still impossible to completely prevent it from penetrating into the bonded area. In addition, such an adhesive of high viscosity causes other problems in that its amount to be applied to the parts to be bonded with it is difficult to control and it requires an expensive dispenser for applying it to the parts to be bonded with it. Naturally, in addition, the thermal expansion of the adhesive for optical use must below, and the latitude in selecting adhesives of desired viscosity for optical use is extremely narrow.
The present invention has been made for solving the problems noted above, and its object is to provide a lens which is easy to produce and has desired optical characteristics, which may be integrated with any other optical device to fabricate small-sized appliances and which suffers little optical loss that may be caused by the adhesive having penetrated into the bonded area of the lens and the additional optical device, and to provide an optical composite structure that comprises the lens.
To attain the object as above, the lens of the invention is so constituted that it comprises a lens face including a convex area that exhibits the lens function thereof and a bonding part formed for bonding an additional optical device to the lens face in another part thereof that is not to be the optical path of the lens.
The optical composite structure of the invention is so constituted that it comprises the lens and an additional optical device bonded thereto, in which the optical device is bonded to the bonding part of the lens with an adhesive.
According to the invention, the light applied to the lens is collimated, conversed or expanded through the convex area formed in the lens face, and therefore, the optical characteristics including the focal length of the lens can be designed in any desired manner by suitably combining the parameters such as the refractive index and the curvature of the convex area of the lens. Accordingly, when the curvature of the convex area of the lens is set large and the focal length thereof is set short, then the lens may be small-sized.
In case where an additional optical device such as a filter is bonded to the lens, it can be accurately positioned on the basis of the bonding part of the lens. Not requiring any specific position control or fixation, the relative position of the lens and the additional optical device can be accurately controlled. Accordingly, the optical composite structure of the invention has the advantages of accurate position control and low optical loss.
Of the lens of the invention, the bonding part is formed in a part of the lens face that is not to be the optical path thereof. Therefore, even when an adhesive is used for bonding an additional optical device to the lens, it is prevented from reaching the optical path of the convex face of the lens to block it. Accordingly, the optical composite structure of the invention suffers little optical loss and its productivity is high.